There are several types of protective covers: engine cowlings, sensor or antenna guards, and covers for auxiliary air intakes such as those for the APU, the air conditioning system, or cooling air intakes.
Their functions may vary depending on the organ they protect.
Engine covers, made from red tarpaulin, help prevent birds from entering and nesting, as well as minimizing the risk of Foreign Object Damage (FOD). They also prevent the blades from spinning while the aircraft is on the ground, which could damage the bearings if they are not lubricated.
Sensor and antenna covers, made of red silicone or polyurethane, protect critical navigation and safety equipment from impacts and prevent insects or ice from clogging them.
Auxiliary air intake shutters, made of rigid composites, elastomers, or plastics, protect these openings from foreign objects.
One thing all these protective covers have in common is that they are red and marked with the words “REMOVE BEFORE FLIGHT.” The pre-flight inspection thus allows for the identification of all equipment that must be removed.